Mesomorphic compound, liquid crystal composition, liquid crystal device, display apparatus and display method

ABSTRACT

A mesomorphic compound represented by the following formula (I): ##STR1## wherein R 1  and R 2  respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with ##STR2## wherein X denotes halogen; X 1  and X 2  respectively denote ##STR3## Z 1  denotes ##STR4## A 1  denotes a single bond, ##STR5## and Y 1  and Y 2  respectively denote H, F, Cl, Br, --CH 3  or --CF 3  with the proviso that Y 1  and Y 2  are not simultaneously H. The mesomorphic compound is effective for providing a ferroelectric liquid crystal composition showing an improved low-temperature operation characteristic and a decreased temperature-dependence of response speed.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a novel mesomorphic compound, a liquid crystal composition a liquid crystal device, a display apparatus and a display method, and more particularly to a novel mesomorphic compound and a liquid crystal composition with improved responsiveness to an electric field, a liquid crystal device using the liquid crystal composition for use in a display device, a liquid crystal-optical shutter, etc., a display apparatus using the device, and a display method using the composition and device.

Hitherto, liquid crystal devices have been used as an electro-optical device in various fields. Most liquid crystal devices which have been put into practice use TN (twisted nematic) type liquid crystals, as shown in "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal" by M. Schadt and W. Helfrich "Applied Physics Letters" Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128.

These devices are based on the dielectric alignment effect of a liquid crystal and utilize an effect that the average molecular axis direction is directed to a specific direction in response to an applied electric field because of the dielectric anisotropy of liquid crystal molecules. It is said that the limit of response speed is on the order of milli-seconds, which is too slow for many uses. On the other hand, a simple matrix system of driving is most promising for application to a large-area flat display in view of cost, productivity, etc., in combination. In the simple matrix system, an electrode arrangement wherein scanning electrodes and signal electrodes are arranged in a matrix, and for driving, a multiplex driving scheme is adopted wherein an address signal is sequentially, periodically and selectively applied to the scanning electrodes and prescribed data signals are selectively applied in parallel to the signal electrodes in synchronism with the address signal.

When the above-mentioned TN-type liquid crystal is used in a device of such a driving system, a certain electric field is applied to regions where a scanning electrode is selected and signal electrodes are not selected or regions where a scanning electrode is not selected and a signal electrode is selected (which regions are so called "half-selected points"). If the difference between a voltage applied to the selected points and a voltage applied to the half-selected points is sufficiently large, and a voltage threshold level required for allowing liquid crystal molecules to be aligned or oriented perpendicular to an electric field is set to a value therebetween, display devices normally operate. However, in fact, as the number (N) of scanning lines increases, a time (duty ratio) during which an effective electric field is applied to one selected point when a whole image area (corresponding to one frame) is scanned decreases with a ratio of 1/N. Accordingly, the larger the number of scanning lines are, the smaller is the voltage difference of an effective value applied to a selected point and non-selected points when scanning is repeatedly effected. As a result, this leads to unavoidable drawbacks of lowering of image contrast or occurrence of interference or crosstalk. These phenomena are regarded as essentially unavoidable problems appearing when a liquid crystal having no bistability (i.e. liquid crystal molecules are horizontally oriented with respect to the electrode surface as stable state and is vertically oriented with respect to the electrode surface only when an electric field is effectively applied) is driven (i.e. repeatedly scanned) by making use of a time storage effect. To overcome these drawbacks, the voltage averaging method, the two-frequency driving method, the multiple matrix method, etc. has been already proposed. However, any method is not sufficient to overcome the above-mentioned drawbacks. As a result, it is the present state that the development of large image area or high packaging density in respect to display elements is delayed because it is difficult to sufficiently increase the number of scanning lines.

To overcome drawbacks with such prior art liquid crystal devices, the use of liquid crystal devices having bistability has been proposed by Clark and Lagerwall (e.g. Japanese Laid-Open Patent Appln. No. 56-107216, U.S. Pat. No. 4,367,924, etc.). In this instance, as the liquid crystals having bistability, ferroelectric liquid crystals having chiral smectic C-phase (SmC*) or H-phase (SmH*) are generally used. These liquid crystals have bistable states of first and second stable states with respect to an electric field applied thereto. Accordingly, as different from optical modulation devices in which the above-mentioned TN-type liquid crystals are used, the bistable liquid crystal molecules are oriented to first and second optically stable states with respect to one and the other electric field vectors, respectively. Further, this type of liquid crystal has a property (bistability) of assuming either one of the two stable states in response to an applied electric and retaining the resultant state in the absence of an electric field.

In addition to the above-described characteristic of showing bistability, such a ferroelectric liquid crystal (hereinafter sometimes abbreviated as "FLC") has an excellent property, i.e., a high-speed responsiveness. This is because the spontaneous polarization of the ferroelectric liquid crystal and an applied electric field directly interact with each other to induce transition of orientation states. The resultant response speed is faster than the response speed due to the interaction between dielectric anisotropy and an electric field by 3 to 4 digits.

Thus, a ferroelectric liquid crystal potentially has very excellent characteristics, and by making use of these properties, it is possible to provide essential improvements to many of the above-mentioned problems with the conventional TN-type devices. Particularly, the application to a high-speed optical shutter and a display of a high density and a large picture is expected. For this reason, there has been made extensive research with respect to liquid crystal materials showing ferroelectricity. However, ferroelectric liquid crystal materials developed heretofore cannot be said to satisfy sufficient characteristics required for a liquid crystal device including low-temperature operation characteristic, high-speed responsiveness, etc. Among a response time τ, the magnitude of spontaneous polarization Ps and viscosity η, the following relationship exists: τ=η/(Ps E), where E is an applied voltage. Accordingly, a high response speed can be obtained by (a) increasing the spontaneous polarization Ps, (b) lowering the viscosity η, or (c) increasing the applied voltage E. However, the driving voltage has a certain upper limit in view of driving with IC, etc., and should desirably be as low as possible. Accordingly, it is actually necessary to lower the viscosity or increase the spontaneous polarization.

A ferroelectric chiral smectic liquid crystal having a large spontaneous polarization generally provides a large internal electric field in a cell given by the spontaneous polarization and is liable to pose many constraints on the device construction giving bistability. Further, an excessively large spontaneous polarization is liable to accompany an increase in viscosity, so that remarkable increase in response speed may not be attained as a result.

Further, if it is assumed that the operation temperature of an actual display device is 5°-40° C., the response speed changes by a factor of about 20, so that it actually exceeds the range controllable by driving voltage and frequency.

As described hereinabove, commercialization of a ferroelectric liquid crystal device requires a liquid crystal composition assuming a chiral smectic phase which has not only a large spontaneous polarization but also a low viscosity, a high-speed responsiveness and a small temperature-dependence of response speed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mesomorphic compound, a liquid crystal composition, particularly a chiral smectic liquid crystal composition, containing the mesomorphic compound for providing a practical ferroelectric liquid crystal device, a liquid crystal device using the liquid crystal composition and having a high response speed and a smaller temperature-dependence of the response speed, a display apparatus using the device, and a display method using the composition and device.

According to the present invention, there is provided a mesomorphic compound represented by the following formula (I): ##STR6## wherein R₁ and R₂ respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with ##STR7## wherein X denotes halogen; X₁ and X₂ respectively denote ##STR8## Z₁ denotes ##STR9## A₁ denotes a single bond, ##STR10## and Y₁ and Y₂ respectively denote H, F, Cl, Br, --CH₃ or --CF₃ with the proviso that Y₁ and Y₂ are not simultaneously H.

According to the present invention, there is further provided a liquid crystal composition containing at least one species of the mesomorphic compound as described above.

The present invention provides a liquid crystal device comprising a pair of electrode plates and the liquid crystal composition described above disposed between the electrode plates.

The present invention further provides a display apparatus comprising the liquid crystal device, and voltage application means for driving the liquid crystal device.

The present invention still further provides a display method using the liquid crystal composition or the liquid crystal device described above and switching the alignment direction of liquid crystal molecules by applying voltages to the liquid crystal composition to effect display.

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a liquid crystal display device using a liquid crystal composition assuming a chiral smectic phase;

FIGS. 2 and 3 are schematic perspective views of a device cell embodiment for illustrating the operation principle of a liquid crystal device utilizing ferroelectricity of a liquid crystal composition;

FIG. 4 is a block diagram showing a display apparatus comprising a liquid crystal device utilizing ferroelectricity of a liquid crystal composition and a graphic controller; and

FIG. 5 is a time chart of image data communication showing time correlation between signal transfer and driving with respect to a liquid crystal display apparatus and a graphic controller.

DETAILED DESCRIPTION OF THE INVENTION

In the formula (I) as described above, preferred examples of X₁ may includes a single bond, ##STR11## particularly a single bond or ##STR12##

Further, X₂ may preferably include a single bond, ##STR13## particularly a single bond and --O--.

Preferred examples of Z₁ may include ##STR14##

Further, R₁ and R₂ each may preferably include the following groups (i) to (iv):

(i) an n-alkyl group having 1-18 carbon atoms, particularly 3-14 carbon atoms;

(ii) ##STR15## wherein m is an integer of 0-7 and n is an integer of 1-9 (optically active or inactive);

(iii) ##STR16## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14 (optically active or inactive); and

(iv) ##STR17## wherein x is an integer of 1-16 (optically active or inactive).

Preferred examples of A₁ may include ##STR18## particularly ##STR19##

Further, Y₁ and Y₂ each may preferably include H, F, Cl, --CH₃ or --CF₃, particularly H or F.

The mesomorphic compounds represented by the general formula (I) may be synthesized through the following reaction schemes. ##STR20##

In the above, R denotes a linear or branched alkyl group optionally substituted. ##STR21##

In the above, R denotes a linear or branched alkyl group optionally substituted and Z₂ denotes --CH₂ OH or --COOH. ##STR22##

In the above, R denotes a linear or branched alkyl group optionally substituted. ##STR23##

Specific examples of the mesomorphic compounds represented by the above-mentioned general formula (I) may include those shown by the following structural formulas. ##STR24##

The liquid crystal composition according to the present invention may be obtained by mixing at least one species of the compound represented by the formula (I) and another mesomorphic compound in appropriate proportions. The liquid crystal composition according to the present invention may preferably be formulated as a liquid crystal composition capable of utilizing ferroelectricity, particularly a liquid crystal composition showing a chiral smectic phase.

Specific examples of another mesomorphic compound as described above may include those denoted by the following formulas (III) to (XI). ##STR25## wherein e denotes 0 or 1 and f denotes 0 or 1 with proviso that e+f=0 or 1; Y' denotes H, halogen, CH₃ or CF₃ ; X₁ ' and X₂ ' respectively denote a single bond, ##STR26## and X₃ ' and X₄ ' respectively denote a single bond, ##STR27##

In the formula (III), preferred compounds thereof may include those represented by the following formulas (IIIa) to (IIId): ##STR28## wherein g and h respectively denote 0 or 1 with proviso that g+h=1; i denotes 0 or 1; X₁ ' and X₂ ' respectively denote a single bond, ##STR29## and X₃ ', X₄ ' and X₅ ' respectively denote a single bond, ##STR30##

In the formula (IV), preferred compounds thereof may include those represented by the following formulas (IVa) to (IVc): ##STR31## wherein j denotes 0 or 1; Y₁ ', Y₂ ' and Y₃ ' respectively denote H, halogen, CH₃ or CF₃ ; X₁ ' and X₂ ' respectively denote a single bond, ##STR32## and X₃ ' and X₄ ' respectively denote a single bond, ##STR33##

In the formula (V), preferred compounds thereof may include those represented by the following formulas (Va) and (Vb): ##STR34## wherein k, l and m respectively denote 0 or 1 with proviso that k+l+m=0, 1 or 2; X₁ ' and X₂ ' respectively denote a single bond, ##STR35## and X₃ ' and X₄ ' respectively denote a single bond, ##STR36## --CH₂ O--or --OCH₂ --.

In the formula (VI), preferred compounds thereof may include those represented by the following formulas (VIa) to (VIf): ##STR37##

Herein, R₁ ' and R₂ ' respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with --CH halogen-- and capable of further including one or two or more non-neighboring methylene groups other than those directly connected to X₁ ' or X₂ ' which can be replaced with at least one species of ##STR38## with proviso that R₁ ' and R₂ ' respectively do not connect to a ring structure by a single bond when R₁ ' and R₂ ' respectively denote a halogenated alkyl group containing one methylene group replaced with --CH halogen--.

Further, preferred examples of R₁ ' and R₂ ' may respectively include those represented by the following groups (i) to (vii):

i) a linear alkyl group having 1-15 carbon atoms;

ii) ##STR39## wherein p denotes an integer of 0-5 and q denotes an integer of 1-11 (optically active or inactive);

iii) ##STR40## wherein r denotes an integer of 0-6, s denotes 0 or 1, and t denotes an integer of 1-14 (optically active or inactive);

iv) ##STR41## wherein u denotes 0 or 1 and v denotes an integer of 1-16; v) ##STR42## wherein w denotes an integer of 1-15 (optically active or inactive); vi) ##STR43## wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and

vii) ##STR44## wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive).

In the above-mentioned formula (III), more preferred compounds thereof may include those represented by the formulas (IIIaa) to (IIIdc): ##STR45##

In the above-mentioned formula (IV), more preferred compounds thereof may include those represented by the formulas (IVaa) to (IVcd): ##STR46##

In the above-mentioned formula (V), more preferred compounds thereof may include those represented by the formulas (Vaa) to (Vbf): ##STR47##

In the above-mentioned formula (VI), more preferred compounds thereof may include those represented by the formulas (VIaa) to (VIfa): ##STR48## wherein E denotes 0 or 1; X₁ ' and X₂ ' respectively denote a single bond, ##STR49## and X₃ ' denotes a single bond, ##STR50## wherein F and G respectively denote 0 or 1; X₁ ' and X₂ ' respectively denote a single bond, ##STR51## and X₃ ' and X₄ ' respectively denote a single bond, ##STR52##

In the above formula (VII), preferred compounds thereof may include those represented by the following formulas (VIIa) and (VIIb): ##STR53##

In the above formula (VIII), preferred compounds thereof may include those represented by the follwoing formulas (VIIIa) and (VIIIb). ##STR54##

More preferred compounds of the formula (VIII) may include those represented by the formulas (VIIIaa) to (VIIIbb): ##STR55##

Herein, R₃ ' and R₄ ' respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with --CH halogen-- and capable of further including one or two or more non-neighboring methylene groups other than those directly connected to X₁ ' or X₂ ' which can be replaced with at least one species of ##STR56## with proviso that R₃ ' and R₄ ' respectively do not connect to a ring structure by a single bond when R₃ ' and R₄ ' respectively denote a halogenated alkyl group containing one methylene group replaced with --CH halogen--.

Further, preferred examples of R₃ ' and R₄ ' may respectively include those represented by the following groups (i) to (vii):

i) a linear alkyl group having 1-15 carbon atoms;

ii) ##STR57## wherein p denotes an integer of 0-5 and q denotes an integer of 1-11 (optically active or inactive);

iii) ##STR58## wherein r denotes an integer of 0-6, s denotes 0 or 1, and t denotes an integer of 1-14 (optically active or inactive);

iv) ##STR59## wherein u denotes an integer of 0 or 1 and v denotes an integer of 1-16; v) ##STR60## wherein w denotes an integer of 1-15 (optically active or inactive); vi) ##STR61## wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and

vii0 ##STR62## wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive). ##STR63## wherein H and J respectively denote 0 or 1 with proviso that H+J=0 or 1; X₁ ' and X₂ ' respectively denote a single bond, ##STR64## A₁ ' denotes ##STR65## and X₃ ' and X₄ ' respectively denote a single bond, ##STR66## wherein X₁ ' and X₂ ' respectively denote a single bond, ##STR67## A₂ ' denotes ##STR68## and X₃ ' and X₄ ' respectively denote a single bond, ##STR69## wherein X₁ ' and X₂ ' respectively denote a single bond, ##STR70## A₃ ' denotes and X₃ ' respectively denotes a single bond, ##STR71##

In the above formula (IX), preferred compounds thereof may include those represented by the following formulas (IXa) to (IXc): ##STR72##

In the above formula (X), preferred compounds thereof may include those represented by the following formulas (Xa) and (Xb): ##STR73##

In the above-mentioned formula (IX), more preferred compounds thereof may include those represented by the formulas (IXaa) to (IXcc): ##STR74##

In the above-mentioned formula (X), more preferred compounds thereof may include those represented by the formulas (Xaa) to (Xbb): ##STR75##

In the above formula (XI), preferred compounds thereof may include those represented by the following formulas (XIa) to (XIg): ##STR76##

Herein, R₅ ' and R₆ ' respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups other than those directly connected to X₁ ' or X₂ ' which can be replaced with at least one species of ##STR77##

Further, preferred examples of R₅ ' and R₆ ' may respectively include those represented by the following groups (i) to (vi):

i) a linear alkyl group having 1-15 carbon atoms;

ii) ##STR78## wherein p denotes an integer of 0-5 and q denotes an integer of 1-11 (optically active or inactive);

iii) ##STR79## wherein r denotes an integer of 0-6, s denotes 0 or 1, and t denotes an integer of 1-14 (optically active or inactive);

iv) ##STR80## wherein w denotes an integer of 1-15 (optically active or inactive); v) ##STR81## wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and

vi) ##STR82## wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive).

In formulating the liquid crystal composition according to the present invention, the liquid crystal composition may desirably contain 1-80 wt. %, preferably 1-60 wt. %, more preferably 1-40 wt. % of a mesomorphic compound represented by the formula (I).

Further, when two or more species of the compounds represented by the formula (I) are used, the liquid crystal composition may desirably contain 1-80 wt. %, preferably 1-60 wt. %, more preferably 1-40 wt. %, of the two or more species of the compounds represented by the formula (I).

The liquid crystal device according to the present invention may preferably be prepared by heating the liquid crystal composition assuming a chiral smectic phase prepared as described above into an isotropic liquid under vacuum, filling a blank cell comprising a pair of oppositely spaced electrode plates with the composition, gradually cooling the cell to form a liquid crystal layer and restoring the normal pressure.

FIG. 1 is a schematic sectional view of an embodiment of the liquid crystal device utilizing ferroelectricity prepared as described above for explanation of the structure thereof.

Referring to FIG. 1, the liquid crystal device includes a liquid crystal layer 1 assuming a chiral smectic phase disposed between a pair of glass substrates 2 each having thereon a transparent electrode 3 and an insulating alignment control layer 4. Lead wires 6 are connected to the electrodes so as to apply a driving voltage to the liquid crystal layer 1 from a power supply 7. Outside the substrates 2, a pair of polarizers 8 are disposed so as to modulate incident light I₀ from a light source 9 in cooperation with the liquid crystal 1 to provide modulated light I.

Each of two glass substrates 2 is coated with a transparent electrode 3 comprising a film of In₂ O₃, SnO₂ or ITO (indium-tin-oxide) to form an electrode plate. Further thereon, an insulating alignment control layer 4 is formed by rubbing a film of a polymer such as polyimide with gauze or acetate fiber-planted cloth so as to align the liquid crystal molecules in the rubbing direction. Further, it is also possible to compose the alignment control layer of two layers, e.g., by first forming an insulating layer of an inorganic material, such as silicon nitride, silicon nitride containing hydrogen, silicon carbide, silicon carbide containing hydrogen, silicon oxide, boron nitride, boron nitride containing hydrogen, cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, or magnesium fluoride, and forming thereon an alignment control layer of an organic insulating material, such as polyvinyl alcohol, polyimide, polyamide-imide, polyester-imide, polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, urea resin, acrylic resin, or photoresist resin. Alternatively, it is also possible to use a single layer of inorganic insulating alignment control layer or organic insulating alignment control layer. An inorganic insulating alignment control layer may be formed by vapor deposition, while an organic insulating alignment control layer may be formed by applying a solution of an organic insulating material or a precursor thereof in a concentration of 0.1 to 20 wt. %, preferably 0.2-10 wt. %, by spinner coating, dip coating, screen printing, spray coating or roller coating, followed by curing or hardening under prescribed hardening condition (e.g., by heating). The insulating alignment control layer may have a thickness of ordinarily 30 Å-1 micron, preferably 30-3000 Å, further preferably 50-1000 Å. The two glass substrates 2 with transparent electrodes 3 (which may be inclusively referred to herein as "electrode plates") and further with insulating alignment control layers 4 thereof are held to have a prescribed (but arbitrary) gap with a spacer 5. For example, such a cell structure with a prescribed gap may be formed by sandwiching spacers of silica beads or alumina beads having a prescribed diameter with two glass plates, and then sealing the periphery thereof with, e.g., an epoxy adhesive. Alternatively, a polymer film or glass fiber may also be used as a spacer. Between the two glass plates, a liquid crystal assuming a chiral smectic phase is sealed up to provide a liquid crystal layer 1 in a thickness of generally 0.5 to 20 microns, preferably 1 to 5 microns.

The ferroelectric liquid crystal provided by the composition of the present invention may desirably assume a SmC* phase (chiral smectic C phase) in a wide temperature range including room temperature (particularly, broad in a lower temperature side) and also shows high-speed responsiveness, a smaller temperature-dependence of response speed and wide drive voltage margin when contained in a device.

Particularly, in order to show a good alignment characteristic to form a uniform monodomain, the ferroelectric liquid crystal may show a phase transition series comprising isotropic phase--Ch phase (cholesteric phase)--SmA phase (smectic C phase)--SmC* phase (chiral smectic C phase) on temperature decrease.

The transparent electrodes 3 are connected to the external power supply 7 through the lead wires 6. Further, outside the glass substrates 2, polarizers 8 are applied. The device shown in FIG. 1 is of a transmission type and is provided with a light source 9.

FIG. 2 is a schematic illustration of a liquid crystal cell (device) utilizing ferroelectricity for explaining operation thereof. Reference numerals 21a and 21b denote substrates (glass plates) on which a transparent electrode of, e.g., In₂ O₃, SnO₂, ITO (indium-tin-oxide), etc., is disposed, respectively. A liquid crystal of an SmC*-phase (chiral smectic C phase) or SmH*-phase (chiral smectic H phase) in which liquid crystal molecular layers 22 are aligned perpendicular to surfaces of the glass plates is hermetically disposed therebetween. Full lines 23 show liquid crystal molecules. Each liquid crystal molecule 23 has a dipole moment (P⊥) 24 in a direction perpendicular to the axis thereof. The liquid crystal molecules 23 continuously form a helical structure in the direction of extension of the substrates. When a voltage higher than a certain threshold level is applied between electrodes formed on the substrates 21a and 21b, a helical structure of the liquid crystal molecule 23 is unwound or released to change the alignment direction of respective liquid crystal molecules 23 so that the dipole moments (P⊥) 24 are all directed in the direction of the electric field. The liquid crystal molecules 23 have an elongated shape and show refractive anisotropy between the long axis and the short axis thereof. Accordingly, it is easily understood that when, for instance, polarizers arranged in a cross nicol relationship, i.e., with their polarizing directions crossing each other, are disposed on the upper and the lower surfaces of the glass plates, the liquid crystal cell thus arranged functions as a liquid crystal optical modulation device of which optical characteristics vary depending upon the polarity of an applied voltage.

Further, when the liquid crystal cell is made sufficiently thin (e.g., less than about 10 microns), the helical structure of the liquid crystal molecules is unwound to provide a non-helical structure even in the absence of an electric field, whereby the dipole moment assumes either of the two states, i.e., Pa in an upper direction 34a or Pb in a lower direction 34b as shown in FIG. 3, thus providing a bistable condition. When an electric field Ea or Eb higher than a certain threshold level and different from each other in polarity as shown in FIG. 3 is applied to a cell having the above-mentioned characteristics by using voltage application means 31a and 31b, the dipole moment is directed either in the upper direction 34a or in the lower direction 34b depending on the vector of the electric field Ea or Eb. In correspondence with this, the liquid crystal molecules are oriented in either of a first stable state 33a and a second stable state 33b.

When the above-mentioned ferroelectric liquid crystal is used as an optical modulation element, it is possible to obtain two advantages. First is that the response speed is quite fast. Second is that the orientation of the liquid crystal shows bistability. The second advantage will be further explained, e.g., with reference to FIG. 3. When the electric field Ea is applied to the liquid crystal molecules, they are oriented in the first stable state 33a. This state is stably retained even if the electric field is removed. On the other hand, when the electric field Eb of which direction is opposite to that of the electric field Ea is applied thereto, the liquid crystal molecules are oriented to the second stable state 33b, whereby the directions of molecules are changed. This state is similarly stably retained even if the electric field is removed. Further, as long as the magnitude of the electric field Ea or Eb being applied is not above a certain threshold value, the liquid crystal molecules are placed in the respective orientation states.

Based on the arrangement and data format comprising image data accompanied with scanning line address data and by adopting communication synchronization using a SYNC signal as shown in FIGS. 4 and 5, there is provided a liquid crystal display apparatus of the present invention which uses the liquid crystal device according to the present invention as a display panel portion.

Referring to FIG. 4, the ferroelectric liquid crystal display apparatus 101 includes a graphic controller 102, a display panel 103, a scanning line drive circuit 104, a data line drive circuit 105, a decoder 106, a scanning signal generator 107, a shift resistor 108, a line memory 109, a data signal generator 110, a drive control circuit 111, a graphic central processing unit (GCPU) 112, a host central processing unit (host CPU) 113, and an image data storage memory (VRAM) 114.

Image data are generated in the graphic controller 102 in an apparatus body and transferred to a display panel 103 by signal transfer means shown in FIGS. 4 and 5. The graphic controller 102 principally comprises a CPU (central processing unit, herein referred to as "GCPU") 112 and a VRAM (video RAM, image data storage memory) 114 and is in charge of management and communication of image data between a host CPU 113 and the liquid crystal display apparatus (FLCD) 101. The control of the display apparatus is principally realized in the graphic controller 102. A light source is disposed at the back of the display panel 103.

Hereinbelow, the present invention will be explained more specifically with reference to examples. It is however to be understood that the present invention is not restricted to these examples.

EXAMPLE 1

4-(5-undecyl-2-pyrimidinyl)-2-fluorophenyl 5-hexylthiophene-2-carboxylate (Example Compound No. 1-65) was synthesized through the following steps 1)-v). ##STR83##

Step i) Production of 2-hexanoylthiophene

In a 5 liter-five-necked flask, 187.3 g (2.23 mol) of thiophene, 300 g (2.23 mol) of n-hexanoyl chloride and 2.7 liter of dry benzene were placed and cooled below 0° C. To the mixture under stirring, 237.9 g (9.13×10⁻¹ mol) of SnCl₄ was added dropwise in 1 hour below 0° C. The mixture was stirred for 30 min. below 0° C., followed by stirring for 3.5 hours while being gradually restored to room temperature. After the reaction, 2 liter of 10% HCl was added to the reaction mixture, followed by stirring for 10 min. The separated organic layer was successively washed three times with 500 ml each of 10% HCl, water, 5% Na₂ CO₃ and water, followed by drying with CaCl₂ and distilling-off of the solvent to obtain 408 g of a crude product. The crude product was subjected to reduced-pressure distillation in an atmosphere of nitrogen to obtain 313.4 g of a pure product (yield: 77.2%).

Step ii) Production of 2-hexylthiophene

In a 10 liter-five-necked flask, 300 g (1.65 mol) of 2-hexanoylthiophene, 582.1 ml of 60% hydrazine hydrate and 5 liter of diethyleneglycol were placed and reacted for 2 hours at 180° C. with distilling-off of excessive water and hydrazine hydrate. The mixture was cooled to 110° C. and 313.7 g of KOH was added thereto, followed by heating again for 2 hours of reaction at 180° C. After the reaction, the reaction mixture was poured into 10 liter of water, extracted two times with 2 liter of isopropyl ether and washed four times with 2 liter of water, followed by drying with CaCl₂ and distilling-off of the solvent to obtain 285 g of a crude product. The crude product was subjected to reduced-pressure distillation in an atmosphere of nitrogen to obtain 230 g of a pure product (yield: 83%).

Step iii) Production of 5-hexylthiophene-2-carbaldehyde

In a 3 liter-four-necked flask, 173.7 (2.38 mol) of N,N-dimethylformamide was placed and cooled to 5° C., followed by addition of 201.4 g (1.31 mol) of POCl₃ in 15 min. below 10° C. under stirring. After stirring for 30 min. below 10° C., 200 g (1.19 mol) of 2-hexylthiophene was added dropwise to the mixture in 10 min. at room temperature, followed by stirring for 1.5 hours and further stirring for 2 hours at 60° C. After the reaction, the reaction mixture was poured into 5 liter of iced water, subjected to 3 times of extraction with 2 liter of chloroform and washed 6 times with 2 liter of water. The organic layer was dried with CaCl₂, followed by distilling-off of the solvent and reduced-pressure distillation in an atmosphere of nitrogen to obtain 199.2 g of a product (yield: 85.0%).

Step iv) Production of 5-hexylthiophene-2-carboxylic acid

In a 5 liter-four-necked flask, 90.0 g (4.59×10⁻¹ mol) of 5-hexylthiophene-2-carbaldehyde, 540 ml of ethanol and a solution of 171.0 g of AgNO₃ in 540 ml of water were placed. A solution of 91.8 g of NaOH in 270 ml of water was added dropwise to the mixture in 30 min. at room temperature, followed by stirring for 1.5 hours. After the reaction, the reaction mixture was subjected to filtration, and the filtrate was acidified with 6N--HCl to precipitate a crystal. The crystal was recovered by filtration to provide a crude product. The product was subjected to recrystallization from 50% hydrous ethanol to obtain 74.5 g of a pure product (yield: 76.6%).

Step v) Production of 4-(5-undecyl-2-pyrimidinyl)-2-fluorophenyl 5-hexylthiophene-2-carboxylate

1.0 g (4.72×10⁻³ mol) of 5-hexylthiophene-2-carboxylic acid, 1.62 g (4.72×10⁻³ mol) 4-(5-undecyl-2-pyrimidinyl)-2-fluorophenol, N,N'-dicyclohexylcarbodiimide (DCC) and 0.03 g of pyrrolidinopyridine were dissolved in 30 ml of dichloromethane, followed by stirring overnight at room temperature. After the reaction, the insoluble matter was filtered off, followed by distilling-off of the solvent to obtain a crude product. The crude product was purified by silica gel column chromatography (eluent: toluene) and recrystallized from a mixture solvent (ethanol/ethyl acetate) to obtain 1.86 g of a pure product (Yield: 3.2%) ##STR84##

Herein, the respective symbols denote the following phases, Iso.:isotropic phase, N:nematic phase, and Cryst.:crystal.

EXAMPLE 2

4-(5-octyl-2-pyrimidinyl)-2-fluorophenyl 5-butylthiophene-2-carboxylate (Example Compound No. I-51) was prepared in the following manner.

0.74 g of the above compound was prepared in the same manner as in Example 1 except for using n-butanoyl chloride instead of n-hexanoyl chloride in the step i) and 4-(5-octyl-2-pyrimidinyl)-2-fluorophenol instead of 4-(5-undecyl-2-pyrimidinyl)-2-fluorophenol in the step v) (Yield: 39.4%). ##STR85##

EXAMPLE 3

4-(5-undecyl-2-pyrimidinyl)-2-fluorophenyl 5-butylthiophene-2-carboxylate (Example Compound No. I-53) was prepared in the following manner.

2.25 g of the above compound was prepared in the same manner as in Example 1 except for using n-butanoyl chloride instead of n-hexanoyl chloride in the step i) (Yield: 81.2%). ##STR86##

EXAMPLE 4

A liquid crystal composition A was prepared by mixing the following compounds in the respectively indicated proportions.

    ______________________________________                                                                       wt.                                              Structural formula            parts                                            ______________________________________                                          ##STR87##                    51.57                                             ##STR88##                    25.79                                             ##STR89##                    12.89                                             ##STR90##                    1.19                                              ##STR91##                    1.19                                              ##STR92##                    2.37                                              ##STR93##                    2.50                                              ##STR94##                    2.50                                             ______________________________________                                    

The liquid crystal composition A was further mixed with the following Example Compound No. I-65 in the proportions indicated below to provide a liquid crystal composition B.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-65                                                                                    ##STR95##                      10                                             Composition A                   90                                     __________________________________________________________________________

The liquid crystal composition B showed the following phase transition series. ##STR96##

EXAMPLE 5

Two 0.7 mm-thick glass plates were provided and respectively coated with an ITO film to form an electrode for voltage application, which was further coated with an insulating layer of vapor-deposited SiO₂. On the insulating layer, a 0.2%-solution of silane coupling agent (KBM-602, available from Shinetsu Kagaku K. K.) in isopropyl alcohol was applied by spinner coating at a speed of 2000 rpm for 15 second and subjected to hot curing treatment at 120° C. for 20 min.

Further, each glass plate provided with an ITO film and treated in the above described manner was coated with a 1.5%-solution of polyimide resin precursor (SP-510, available from Toray K. K.) in dimethylacetoamide by a spinner coater rotating at 2000 rpm for 15 seconds. Thereafter, the coating film was subjected to heat curing at 300° C. for 60 min. to obtain about 250 Å-thick film. The coating film was rubbed with acetate fiber-planted cloth. The thus treated two glass plates were washed with isopropyl alcohol. After alumina beads with an average particle size of 2.0 microns were dispersed on one of the glass plates, the two glass plates were applied to each other with a bonding sealing agent (Lixon Bond, available from Chisso K. K.) so that their rubbed directions were parallel to each other and heated at 100° C. for 60 min. to form a blank cell. The cell gap was found to be about 2 microns as measured by a Berek compensator.

Then, the liquid crystal composition B prepared in Example 4 was heated into an isotropic liquid, and injected into the above prepared cell under vacuum and, after sealing, was gradually cooled at a rate of 20° C./hour to 25° C. to prepare a ferroelectric liquid crystal device.

The ferroelectric liquid crystal device was subjected to measurement of the magnitude of spontaneous polarization Ps and an optical response time (time from voltage application until the transmittance change reaches 90% of the maximum under the application of a peak-to-peak voltage Vpp of 20 V in combination with right-angle cross-nicol polarizers).

The results are shown below.

    ______________________________________                                                      10° C.                                                                           30° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       383        182     114                                          Ps (nC/cm.sup.2)                                                                              2.58       1.71    1.03                                         ______________________________________                                    

EXAMPLE 6

A liquid crystal composition C was prepared by mixing the following example compound No. I-53 with the liquid crystal composition A prepared in Example 4 in the indicated proportions.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-53                                                                                    ##STR97##                      10                                             Composition A                   90                                     __________________________________________________________________________

The liquid crystal composition C showed the following phase transition series. ##STR98##

EXAMPLE 7

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except for using the composition C. The ferroelectric liquid crystal device was subjected to measurement of the magnitude of spontaneous polarization Ps and response time in the same manner as in Example 5, whereby the following results were obtained.

    ______________________________________                                                      10° C.                                                                           30° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       362        177     96                                           Ps (nC/cm.sup.2)                                                                              3.19       2.05    1.67                                         ______________________________________                                    

EXAMPLE 8

A liquid crystal composition D was prepared by mixing the following compounds in the respectively indicated proportions.

    __________________________________________________________________________     Structural formula                  wt. parts                                  __________________________________________________________________________      ##STR99##                          12                                          ##STR100##                         10                                          ##STR101##                         10                                          ##STR102##                         3                                           ##STR103##                         8                                           ##STR104##                         4                                           ##STR105##                         6                                           ##STR106##                         2                                           ##STR107##                         8                                           ##STR108##                         15                                          ##STR109##                         7                                           ##STR110##                         7                                           ##STR111##                         4                                           ##STR112##                         2                                           ##STR113##                         2                                          __________________________________________________________________________

The liquid crystal composition D was further mixed with the following Example Compounds in the proportions indicated below to provide a liquid crystal composition E.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-16                                                                                    ##STR114##                     2                                      I-46                                                                                    ##STR115##                     4                                      I-65                                                                                    ##STR116##                     4                                              Composition D                   90                                     __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except for using the composition E. The ferroelectric liquid crystal device was subjected to measurement of response time in the same manner as in Example 5, whereby the following results were obtained.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       658        337     197                                          ______________________________________                                    

COMPARATIVE EXAMPLE 1

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the liquid crystal composition D prepared in Example 8 was injected into a cell. The measured values of the response time of the device were as follows.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       784        373     197                                          ______________________________________                                    

EXAMPLE 9

A liquid crystal composition F was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition D prepared in Example 8.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula               wt. parts                             __________________________________________________________________________     I-20                                                                                    ##STR117##                      3                                     I-29                                                                                    ##STR118##                      3                                     I-64                                                                                    ##STR119##                      3                                             Composition D                    91                                    __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition F was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       621        315     183                                          ______________________________________                                    

EXAMPLE 10

A liquid crystal composition G was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition D prepared in Example 8.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-15                                                                                    ##STR120##                     4                                      I-57                                                                                    ##STR121##                     2                                              Composition D                   94                                     __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition G was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       720        353     199                                          ______________________________________                                    

EXAMPLE 11

A liquid crystal composition H was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition D prepared in Example 8.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-72                                                                                    ##STR122##                     4                                      I-85                                                                                    ##STR123##                     2                                       I-106                                                                                  ##STR124##                     2                                              Composition D                   92                                     __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition H was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       669        334     189                                          ______________________________________                                    

EXAMPLE 12

A liquid crystal composition I was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition D prepared in Example 8.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula               wt. parts                             __________________________________________________________________________     I-5                                                                                     ##STR125##                      3                                     I-126                                                                                   ##STR126##                      3                                     I-134                                                                                   ##STR127##                      4                                             Composition D                    90                                    __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition I was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       665        335     191                                          ______________________________________                                    

EXAMPLE 13

A liquid crystal composition J was prepared by mixing the following compounds in the respectively indicated proportions.

    __________________________________________________________________________     Structural formula               wt. parts                                     __________________________________________________________________________      ##STR128##                      10                                             ##STR129##                      5                                              ##STR130##                      7                                              ##STR131##                      7                                              ##STR132##                      6                                              ##STR133##                      5                                              ##STR134##                      5                                              ##STR135##                      8                                              ##STR136##                      8                                              ##STR137##                      20                                             ##STR138##                      5                                              ##STR139##                      5                                              ##STR140##                      6                                              ##STR141##                      3                                             __________________________________________________________________________

The liquid crystal composition J was further mixed with the following Example Compounds in the proportions indicated below to provide a liquid crystal composition K.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula               wt. parts                             __________________________________________________________________________     I-22                                                                                    ##STR142##                      3                                     I-53                                                                                    ##STR143##                      4                                     I-77                                                                                    ##STR144##                      3                                             Composition J                    90                                    __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition K was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       560        292     163                                          ______________________________________                                    

COMPARATIVE EXAMPLE 2

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the liquid crystal composition J prepared in Example 13 was injected into a cell. The measured values of the response time of the device were as follows.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       653        317     159                                          ______________________________________                                    

EXAMPLE 14

A liquid crystal composition L was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition J prepared in Example 13.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula                wt. parts                            __________________________________________________________________________     I-75                                                                                    ##STR145##                       2                                    I-145                                                                                   ##STR146##                       3                                    I-155                                                                                   ##STR147##                       2                                            Composition J                     93                                   __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition L was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       584        290     155                                          ______________________________________                                    

EXAMPLE 15

A liquid crystal composition M was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition J prepared in Example 13.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula                   wt. parts                         __________________________________________________________________________     I-2                                                                                     ##STR148##                          4                                 I-38                                                                                    ##STR149##                          2                                 I-10                                                                                    ##STR150##                          2                                         Composition J                        92                                __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition M was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       586        291     155                                          ______________________________________                                    

EXAMPLE 16

A liquid crystal composition N was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition J prepared in Example 13.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula               wt. parts                             __________________________________________________________________________     I-12                                                                                    ##STR151##                      3                                     I-70                                                                                    ##STR152##                      2                                             Composition J                    95                                    __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition N was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       596        295     156                                          ______________________________________                                    

EXAMPLE 17

A liquid crystal composition O was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition J prepared in Example 13.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula                wt. parts                            __________________________________________________________________________     I-4                                                                                     ##STR153##                       2                                    I-47                                                                                    ##STR154##                       2                                    I-140                                                                                   ##STR155##                       3                                            Composition J                     93                                   __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition O was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       560        282     147                                          ______________________________________                                    

EXAMPLE 18

A liquid crystal composition P was prepared by mixing the following compounds in the respectively indicated proportions.

    __________________________________________________________________________     Structural formula               wt. parts                                     __________________________________________________________________________      ##STR156##                      6                                              ##STR157##                      6                                              ##STR158##                      7                                              ##STR159##                      14                                             ##STR160##                      8                                              ##STR161##                      4                                              ##STR162##                      2                                              ##STR163##                      10                                             ##STR164##                      5                                              ##STR165##                      10                                             ##STR166##                      7                                              ##STR167##                      7                                              ##STR168##                      5                                              ##STR169##                      2                                              ##STR170##                      2                                              ##STR171##                      2                                              ##STR172##                      3                                             __________________________________________________________________________

The liquid crystal composition P was further mixed with the following Example Compounds in the proportions indicated below to provide a liquid crystal composition Q.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-31                                                                                    ##STR173##                     2                                      I-51                                                                                    ##STR174##                     3                                      I-62                                                                                    ##STR175##                     4                                              Composition P                   91                                     __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition Q was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       571        310     181                                          ______________________________________                                    

COMPARATIVE EXAMPLE 3

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the liquid crystal composition P prepared in Example 18 was injected into a cell. The measured values of the response time of the device were as follows.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       668        340     182                                          ______________________________________                                    

EXAMPLE 19

A liquid crystal composition R was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition P prepared in Example 18.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula              wt. parts                              __________________________________________________________________________     I-13                                                                                    ##STR176##                     2                                      I-80                                                                                    ##STR177##                     2                                      I-150                                                                                   ##STR178##                     5                                              Composition P                   91                                     __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition R was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       558        298     172                                          ______________________________________                                    

EXAMPLE 20

A liquid crystal composition S was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition P prepared in Example 18.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula                wt. parts                            __________________________________________________________________________     I-44                                                                                    ##STR179##                       3                                    I-131                                                                                   ##STR180##                       4                                            Composition P                     93                                   __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition S was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       447        236     132                                          ______________________________________                                    

EXAMPLE 21

A liquid crystal composition T was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition P prepared in Example 18.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula                wt. parts                            __________________________________________________________________________     I-17                                                                                    ##STR181##                       2                                    I-90                                                                                    ##STR182##                       2                                    I-158                                                                                   ##STR183##                       2                                            Composition P                     94                                   __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition T was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       587        310     179                                          ______________________________________                                    

EXAMPLE 22

A liquid crystal composition U was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition P prepared in Example 18.

    __________________________________________________________________________     Ex. Comp. No.                                                                          Structural formula                 wt. parts                           __________________________________________________________________________     I-92                                                                                    ##STR184##                        2                                   I-99                                                                                    ##STR185##                        3                                   I-168                                                                                   ##STR186##                        2                                           Composition P                      93                                  __________________________________________________________________________

A ferroelectric liquid crystal device was prepared in the same manner as in Example 5 except that the above liquid crystal composition U was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       599        321     186                                          ______________________________________                                    

EXAMPLE 23

A blank cell was prepared in the same manner as in Example 8 by using a 2% aqueous solution of polyvinyl alcohol resin (PVA-117, available from Kuraray K. K.) instead of the 1.5%-solution of polyimide resin precursor in dimethylacetoamide on each electrode plate. A ferroelectric liquid crystal device was prepared by filling the blank cell with the liquid crystal composition E prepared in Example 8. The liquid crystal device was subjected to measurement of optical response time in the same manner as in Example 5. The results are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       631        322     186                                          ______________________________________                                    

EXAMPLE 24

A blank cell was prepared in the same manner as in Example 8 except for omitting the SiO₂ layer to form an alignment control layer composed of the polyimide resin layer alone on each electrode plate. A ferroelectric liquid crystal device was prepared by filling the blank cell with the liquid crystal composition E prepared in Example 8. The liquid crystal device was subjected to measurement of optical response time in the same manner as in Example 5. The results are shown below.

    ______________________________________                                                      10° C.                                                                           25° C.                                                                          40° C.                                    ______________________________________                                         Response time (μsec)                                                                       604        307     178                                          ______________________________________                                    

As is apparent from the above Examples 23 and 24, also in the cases of different device structures, the devices containing the ferroelectric liquid crystal composition H according to the present invention respectively provided a remarkably improved operation characteristic at a lower temperature and also a decreased temperature-dependence of the response speed similar to those in Example 8.

EXAMPLE 25

4-(5-octyl-2-pyrimidinyl)-2-fluorophenyl 5-octylthiophene-2-carboxylate (Example Compound No. I-75) was prepared in the following manner.

1.62 g of the above compound was prepared in the same manner as in Example 1 except for using n-octanoyl chloride instead of n-hexanoyl chloride in the step i) and 4-(5-octyl-2-pyrimidinyl)-2-fluorophenol instead of 4-(5-undecyl-2-pyrimidinyl)-2-fluorophenol in the step v) (Yield: 76.8%). ##STR187##

EXAMPLE 26

4-(5-decyl-2-pyrimidinyl)-2-fluorophenyl 5-hexylthiophene-2-carboxylate (Example Compound No. 1-181) was prepared in the following manner.

1.79 g of the above compound was prepared in the same manner as in Example 1 except for using 4-(5-decyl-2-pyrimidinyl)-2-fluorophenol instead of 4-(5-undecyl-2-pyrimidinyl)-2-fluorophenol in the step v) (Yield: 74.9%). ##STR188##

As described hereinabove, according to the present invention, there is provided a mesomorphic compound which can effectively be applied to a liquid crystal device utilizing ferroelectricity when the compound per se assumes a chiral smectic phase. Further, there is also provided a liquid crystal composition containing the compound and assuming a chiral smectic phase, whereby a liquid crystal device comprising the composition can be operated by utilizing ferroelectricity of the composition. The present invention provides a liquid crystal device using such a composition which shows a good switching characteristic, an improved low-temperature operation characteristic and a decreased temperature-dependence of response speed. The present invention further provides a display apparatus and a display method which employ such a device as a display unit, whereby good display characteristics can be obtained in combination with a light source, a drive circuit, etc. 

What is claimed is:
 1. A mesomorphic compound represented by the following formula (I): ##STR189## wherein R₁ and R₂ independently denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with ##STR190## wherein X denotes halogen; X₁ and X₂ independently denote a single bond, ##STR191## Z₁ denotes ##STR192## A₁ denotes a single bond, ##STR193## and Y₁ and Y₂ independently denote H, F, Cl, Br, --CH₃ or --CF₃ with the proviso that at least one Y₁ and Y₂ is.
 2. A mesomorphic compound according to claim 1, wherein X₁ denotes a single bond, ##STR194##
 3. A mesomorphic compound according to claim 1, wherein X₂ denotes a single bond or --O--.
 4. A mesomorphic compound according to claim 1, wherein Z₁ denotes ##STR195##
 5. A mesomorphic compound according to claim 1, wherein R₁ and R₂ respectively denote any one of the following groups (i) to (iv):(i) an n-alkyl group having 1-18 carbon atoms; (ii) ##STR196## wherein m is an integer of 0-7 and n is an integer of 1-9; (iii) ##STR197## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14; and (iv) ##STR198## wherein x is an integer of 1-16.
 6. A mesomorphic compound according to claim 1, wherein A₁ denotes ##STR199##
 7. A mesomorphic compound according to claim 1, wherein Y₁ and Y₂ respectively denote H or F.
 8. A mesomorphic compound according to claim 1, which is an optically active compound.
 9. A mesomorphic compound according to claim 1, which is an optically inactive compound.
 10. A liquid crystal composition comprising at least two mesomorphic compounds, at least one of which is a mesomorphic compound of the formula (I) according to claim
 1. 11. A liquid crystal composition according to claim 10, which comprises 1-80 wt. % of a mesomorphic compound of the formula (I).
 12. A liquid crystal composition according to claim 10, which comprises 1-60 wt. % of a mesomorphic compound of the formula (I).
 13. A liquid crystal composition according to claim 10, which comprises 1-40 wt. % of a mesomorphic compound of the formula (I).
 14. A liquid crystal composition according to claim 10, which is a chiral smectic phase.
 15. A liquid crystal composition according to claim 10, wherein X₁ in the formula (I) denotes a single bond, ##STR200##
 16. A liquid crystal composition according to claim 10, wherein X₂ in the formula (I) denotes a single bond or --O--.
 17. A liquid crystal composition according to claim 10, wherein Z₁ in the formula (I) denotes ##STR201##
 18. A liquid crystal composition according to claim 10, wherein R₁ and R₂ in the formula (I) respectively denote any one of the following groups (i) to (iv):(i) an n-alkyl group having 1-18 carbon atoms; (ii) ##STR202## wherein m is an integer of 0-7 and n is an integer of 1-9; (iii) ##STR203## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14; and (iv) ##STR204## wherein x is an integer of 1-16.
 19. A liquid crystal composition according to claim 10, wherein A₁ in the formula (I) denotes ##STR205##
 20. A liquid crystal composition according to claim 10, wherein Y₁ and Y₂ respectively denote H or F.
 21. A liquid crystal device, comprising a pair of electrode plates and a liquid crystal composition according to claim 10 disposed between the electrode plates.
 22. A liquid crystal device according to claim 21, wherein X₁ in the formula (I) denotes a single bond, ##STR206##
 23. A liquid crystal device according to claim 21, wherein X₂ in the formula (I) denotes a single bond or --O--.
 24. A liquid crystal device according to claim 21, wherein Z₁ in the formula (I) denotes ##STR207##
 25. A liquid crystal device according to claim 21, wherein R₁ and R₂ in the formula (I) respectively denote any one of the following groups (i) to (iv):(i) an n-alkyl group having 1-18 carbon atoms; (ii) ##STR208## wherein m is an integer of 0-6 and n is an integer of 1-9; (iii) ##STR209## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14; and (iv) ##STR210## wherein x is an integer of 1-16.
 26. A liquid crystal device according to claim 21, wherein A₁ in the formula (I) denotes ##STR211##
 27. A liquid crystal device according to claim 21, wherein Y₁ and Y₂ respectively denote H or F.
 28. A liquid crystal device according to claim 21, which further comprises an insulating alignment control layer.
 29. A liquid crystal device according to claim 28, wherein the insulating alignment control layer has been subjected to rubbing.
 30. A display apparatus comprising a liquid crystal device according to claim 21, and voltage application means for driving the liquid crystal device.
 31. A display apparatus according to claim 30, wherein X₁ in the formula (I) denotes a single bond, ##STR212##
 32. A display apparatus according to claim 30, wherein X₂ in the formula (I) denotes a single bond or --O--.
 33. A display apparatus according to claim 30, wherein Z₁ in the formula (I) denotes ##STR213##
 34. A display apparatus according to claim 30, wherein R₁ and R₂ in the formula (I) respectively denote any one of the following groups (i) to (iv):(i) an n-alkyl group having 1-18 carbon atoms; (ii) ##STR214## wherein m is an integer of 0-7 and n is an integer of 1-9; (iii) ##STR215## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14; and (iv) ##STR216## wherein x is an integer of 1-16.
 35. A display apparatus according to claim 30, wherein A₁ in the formula (I) denotes ##STR217##
 36. A display apparatus according to claim 30, wherein Y₁ and Y₂ respectively denote H or F.
 37. A display apparatus according to claim 34, which further comprises a drive circuit.
 38. A display apparatus according to claim 34, which further comprises a light source.
 39. A display method, comprising:providing a liquid crystal composition comprising at least two mesomorphic compound, at least one of which is a mesomorphic compound of the following formula (I): ##STR218## wherein R₁ and R₂ independently denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with ##STR219## wherein X denotes halogen; X₁ and X₂ independently denote a single bond, ##STR220## Z₁ denotes ##STR221## A₁ denotes a single bond, ##STR222## and Y₁ and Y₂ independently denote H, F, Cl, Br, --CH₃ or --CF₃ with the proviso that at least one of Y₁ and Y₂ is F; and switching the alignment direction of liquid crystal molecules by applying voltages to the liquid crystal composition to effect display.
 40. A display method according to claim 39, wherein X₁ in the formula (I) denotes a single bond, ##STR223##
 41. A display method according to claim 39, wherein X₂ in the formula (I) denotes a single bond or --O--.
 42. A display method according to claim 39, wherein Z₁ in the formula (I) denotes ##STR224##
 43. A display method according to claim 39, wherein R₁ and R₂ in the formula (I) respectively denote any one of the following groups (i) to (iv):(i) an n-alkyl group having 1-18 carbon atoms; (ii) ##STR225## wherein m is an integer of 0-7 and n is an integer of 1-9; (iii) ##STR226## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14; and (iv) ##STR227## wherein x is an integer of 1-16.
 44. A display method according to claim 39, wherein A₁ in the formula (I) denotes ##STR228##
 45. A display method according to claim 39, wherein Y₁ and Y₂ respectively denote H or F.
 46. A display method according to claim 39, which is an optically active compound.
 47. A display method according to claim 39, which is an optically inactive compound.
 48. A display method according to claim 39, wherein the liquid crystal composition comprises 1-80 wt. % of a mesomorphic compound of the formula (I).
 49. A display method according to claim 39, wherein the liquid crystal composition comprises 1-60 wt. % of a mesomorphic compound of the formula (I).
 50. A display method according to claim 39, wherein the liquid crystal composition comprises 1-40 wt. % of a mesomorphic compound of the formula (I).
 51. A display method according to claim 39, wherein the liquid crystal composition assumes a chiral smectic phase.
 52. A display method, comprising:providing a liquid crystal device comprising a pair of electrode plates and a liquid crystal composition disposed therebetween comprising at least two mesomorphic compound, at least one of which is a mesomorphic compound of the following formula (I): ##STR229## wherein R₁ and R₂ independently denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or two or more non-neighboring methylene groups which can be replaced with ##STR230## wherein X denotes halogen; X₁ and X₂ independently denote a single bond ##STR231## Z₁ denotes ##STR232## A₁ denotes a single bond, ##STR233## and Y₁ and Y₂ independently denote H, F, Cl, Br, --CH₃ or --CF₃ with the proviso that at least one of Y₁ and Y₂ is F; and switching the alignment direction of liquid crystal molecules by applying voltages to the liquid crystal composition between the electrode plates to effect display.
 53. A display method according to claim 52, wherein X₁ in the formula (I) denotes a single bond, ##STR234##
 54. A display method according to claim 52, wherein X₂ in the formula (I) denotes a single bond or --O--.
 55. A display method according to claim 52, wherein Z₁ in the formula (I) denotes ##STR235##
 56. A display method according to claim 52, wherein R₁ and R₂ in the formula (I) respectively denote any one of the following groups (i) to (iv):(i) an n-alkyl group having 1-18 carbon atoms; (ii) ##STR236## wherein m is an integer of 0-7 and n is an integer of 1-9; (iii) ##STR237## wherein r is an integer of 0-7, s is 0 or 1, and t is an integer of 1-14; and (iv) ##STR238## wherein x is an integer of 1-16.
 57. A display method according to claim 52, wherein A₁ in the formula (I) denotes ##STR239##
 58. A display method according to claim 52, wherein Y₁ and Y₂ respectively denote H or F.
 59. A display method according to claim 52, which is an optically active compound.
 60. A display method according to claim 52, which is an optically inactive compound. 